Solar Concentration Systems (SCS) are used to increase the flux density of solar radiation so that the temperatures reached by the working fluid are those required for its use in industrial processes and in processes of power generation.
Within the SCS there are the Tower Central Receiver Systems, where solar radiation is concentrated by using heliostats in a receiver located on top of a tower (in the focus of the optical system) and where it is transformed into thermal energy by the absorption of heat from the working fluid.
A first approach to the tower central receiver technology was defined in the U.S. Pat. No. 3,924,604, 1974; the receiver described there, exterior-type and with tubes arranged around the central axis of the tower, is located on top of the same, which in turn is located in the middle of a field of heliostats arranged circularly. Later, in 1983, a new configuration for a tower solar concentration plant was described by the U.S. Pat. No. 4,400,946, where steam generation in a receiver arranged in a ring of a circular sector of the circle described by the tower was set forth; since then, other patents have been published regarding this technology seeking to optimize the various elements and processes of the system, such as U.S. Pat. No. 6,911,110 and WO2008118980, published in 2005 and 2008 respectively.
Currently, commercial demonstration projects using cavity-type receivers can be found. One of the most outstanding projects in this field is that of PS10 in Seville, which has a saturated steam cavity receiver. On the other hand, the Plataforma Solar de Almeria, where the project CESA-I was developed, has the necessary infrastructure for carrying out the testing of pilot-sized solar components among which volumetric type receivers have been tested, wherein is used air as heat-transfer fluid. The design of these devices should be done such as to optimize their operation, thus preventing both heat loss (especially by radiation and convection) and the pressure drops. Patent ES2168992 published in 2002, refers to the use of volumetric receivers in solar concentration systems.
The saturated steam tower technologies currently available require the use of drive pumps to increase the working fluid to the receiver, and this causes that the pressure drops are much greater than those resulting from the system proposed in this invention.
However, in the case of plants producing electricity with fossil fuel, there is the concept of natural circulation, since in these the dimensions of the drums are much larger and facilitate the application of this phenomenon.
In the case of solar receivers the dimensions handled are much smaller and do not facilitate the natural circulation.
This invention pose the use of natural circulation with a new design of components that helps reduce circuit pressure drops, as an alternative to increase the efficiency of the system.
Its implementation will allow the recirculation of the fluid to be carried out without the use of pumps.
The proposed innovation seeks to exploit one of the physical properties of the working fluid (density) in the operating conditions which, under a proper configuration of the circuit components (equipment elevations, lengths and diameters of tubes), can result in the natural circulation phenomenon. The introduction of this improvement makes more feasible to use technology at commercial production levels since the recirculation of water through a closed circuit is achieved, without requiring pumps, reducing self-consumption of the plant (electricity consumption of auxiliary components) and increasing the net production of electricity of the same.
Thus, there is proposed a new improvement both for the receiver as a component of the solar concentration system, and for the processes involved in the generation of saturated steam. The design of a tower solar receiver for the generation of saturated steam with natural circulation is completely novel and unique in the world.